1. Field of the Invention
The present invention relates to transmission mechanisms for vehicles having an HST (hydrostatic transmission), and more particularly to a transmission mechanism for work vehicles equipped with a work device externally of the vehicle body, and also to a pressure oil supply system for the mechanism.
2. Description of the Related Technology
It is commonly demanded that various vehicles be shortened in forward or rearward length to diminish the turning radius, improve the ease of driving and achieve cost reductions. Especially, this is strongly demanded of work vehicles which are equipped with a work device externally of the vehicle body in front or in the rear thereof.
Work vehicles provided with a work device externally of the vehicle body have a PTO shaft at a portion of the transmission for transmitting power to the work device. With such work vehicles, it is desired that the transmission shaft interconnecting the PTO shaft and the input shaft of the work device be disposed horizontally to the greatest possible extent in order to prevent the joints of the transmission shaft from giving off noise and assure the joints of improved durability. For example, JP-U1 No. 56555/1993 and JP-A No. 204135/1990 disclose transmissions for work vehicles intended to meet this demand. The disclosed arrangements include pulleys or like cooperative means for positioning a PTO shaft 1103 at a lower level than a front axle 1105 to cause the shaft to project from the front end face of the front axle case (as indicated at X in FIG. 19). Generally, the transmission shaft 1104 for a work device 1106 needs to be lengthened (as indicated at Y in FIG. 19) if it is attempted to position the transmission shaft 1104 closer to a horizontal while causing the PTO shaft 1103, as positioned approximately at the same level as the engine drive shaft 1101a, to project from the front end of the front axle case, consequently increasing the overall vehicle length. Alternatively, the transmission shaft 1104 must be inclined (as indicated at Z in FIG. 19) if an attempt is made to shorten the overall vehicle length while causing the PTO shaft 1103 to project from the front end of the front axle case at substantially the same level as the engine drive shaft 1101a, consequently increasing the load on the transmission shaft and impairing the durability of the transmission shaft. In view of these structural drawbacks, the transmissions disclosed in the foregoing publications are so constructed as stated above.
In the case of the conventional construction described, however, a differential gear unit is to be interposed between the engine output shaft (or HST motor shaft) and the PTO shaft, so that the cooperative mechanism between the two shafts must be adapted to avoid the interference with the differential gear unit. This results in an increase in the vehicle cost and an impaired maintenance work efficiency.
With vehicles, especially with work vehicles, it is known to dividedly derive a rear wheel driving force from the output of an HST for driving the front wheels. JPA No. 66749/1997, for example, discloses such a transmission mechanism. With reference to FIG. 20 showing such a conventional transmission mechanism as is disclosed in this publication, a vehicle comprising a differential gear unit 1140, HST 1120 and drive source 1110 which are arranged from the front of the vehicle rearward has a transmission 1130, in which a driving force from the drive source is divided into a front wheel driving force and a rear wheel driving force. This construction has the following drawbacks. Incidentally, indicated at 1131 in the drawing is a front wheel drive shaft which is coupled to the differential gear unit 1140 for driving front axles 1151, and at 1132 is a rear wheel drive shaft which is connected to a rear axle 1152 by an unillustrated transmission shaft.
The transmission mechanism shown in FIG. 20 essentially requires the transmission 1130, which increases the number of parts and the cost. The provision of the transmission 1130 further entails the problem of impairing the reliability of the vehicle. Since the transmission 1130 serves as a power transmission path for both the front wheel driving force and the rear wheel driving force, the components of the transmission are burdened with a great load. Accordingly, the gears and other components are susceptible to damage, which lowers the reliability of the vehicle. Furthermore, the transmission 1130 is provided in a limited space between the differential gear unit 1140 and the HST 1130, necessitating difficult installation work, which leads to the problem that the vehicle is inefficient to assemble in its entirety.
With work vehicles equipped with a work device externally of the vehicle body, there is a need to provide a considerable distance between the engine and the HST because it is necessary to interconnect the drive source and the HST by means of universal joints. Stated more specifically, the drive source is installed on the vehicle body with rubber vibration isolators interposed therebetween, while the HST is connected to the differential gear casing which is fixed to the front axle cases. A vibration difference therefore occurs between the drive source and the HST. Accordingly, to interconnect the two components by a shaft with the vibration difference absorbed, universal joints are used for the shaft to be connected between the drive source and the HST. For this reason, there is a need to provide a distance permitting the arrangement of two universal joints in series between the HST and the drive source.
With vehicles wherein a PTO unit is provided which has a PTO shaft for a mower or like work device, and a hydraulic clutch for effecting or interrupting the transmission of the output of the PTO shaft, it is desired to position the PTO shaft inwardly of the vehicle body to the greatest possible extent while shortening the distance between the hydraulic clutch and a charge pump for supplying a hydraulic fluid to the clutch.
A shorter distance between the pump and the clutch is desirable because of the difficulty to be encountered in hydraulically controlling the clutch if the distance is great. Inward positioning of the PTO shaft is desirable in order to reduce the overall length of the vehicle including the mower or the like while horizontally positioning the connecting rod between the shaft and the mower or the like.
This will be described with reference to a front mount mower tractor which is equipped with a mower in front of the vehicle body. If it is attempted to shorten the overall length of the vehicle including the mower in an arrangement wherein the PTO shaft is caused to project forward from the front axle case, the transmission shaft interconnecting the PTO shaft and the mower must be given a great inclination. The transmission shaft is pivotally moved vertically when the mower is raised or lowered. If the inclination of the transmission shaft is greater, the angle through which the shaft is pivotally moved also increases, permitting the transmission shaft joints to produce a louder noise and impairing the durability of the joints. It is therefore desired that the PTO shaft be disposed inward longitudinally of the vehicle body (toward the rear of the vehicle body in the case of the front mount mower tractor) in order to shorten the overall length of the vehicle while obviating these drawbacks.
Thus, it is desired that the vehicle wherein the power of the drive source is transmitted to the travel device and to the PTO unit via the HST fulfill the foregoing requirements, whereas transmission mechanisms still remain to be developed which meet all of these requirements.
Conventionally, the following construction has been adopted for the pressure oil supply system for supplying a hydraulic fluid to power steering hydraulic devices or to hydraulic devices for lifting work devices such as mowers. The conventional pressure oil supply system has an arrangement wherein a hydraulic pump for supplying the pressure oil is attached to the drive source of the vehicle, and the casing of the differential gear unit is used also as an oil tank serving as the oil supply source for the hydraulic pump. The pump shaft of the hydraulic pump can be coupled to the drive source easily, while the use of the casing eliminates the cost increase and the increase of the vehicle size that would result if an oil tank for specific use is provided.
However, this arrangement requires an elongated inflow line interconnecting the hydraulic pump and the casing, consequently offering the piping increased resistance which is liable to impair the operation efficiency of the pump. Although the inflow line can be given an increased diameter to reduce the piping resistance, this will entail an increased cost.
The drive source is installed in the vehicle body with use of rubber vibration isolators, while the casing is fixed to the axle case, so that a vibration difference occurs between the hydraulic pump attached to the drive source and the casing. This results in the necessity of using a flexible tube or like pipe which is capable of absorbing the vibration difference between the pump and the casing for the inflow line for holding these two components in communication, hence a higher cost.
In order to shorten the distance between the hydraulic pump and the oil tank, it is possible to install a specific tank in the vehicle, as positioned in a vacant space in the vicinity of the drive source, but the installation of the specific tank leads to a higher cost and a greater vehicle size. Use of such a tank still involves the problem of vibration difference between the oil tank and the hydraulic pump.
Summary of Certain Inventive Aspects
A first object of the present invention is to provide a transmission mechanism which is simple in construction for use in work vehicles equipped with a work device externally of the vehicle body, the transmission mechanism being adapted to shorten the overall length of the vehicle.
A second object of the invention is to provide a transmission mechanism for use in such work vehicles which is adapted to shorten the overall length of the vehicle body while permitting a transmission shaft to be positioned close to a horizontal for interconnecting a PTO shaft for driving the work device and the input shaft of the work device.
A third object of the invention is to provide a transmission mechanism of simple construction for the front wheels and rear wheels of vehicles including an HST, the transmission mechanism comprising components which are rendered free of excessive loads.
A fourth object of the invention is to provide a transmission mechanism which realizes at the same time a vehicle of shortened overall length, positioning of a PTO shaft longitudinally inwardly of the vehicle body and provision of a sufficient distance between the drive source and an HST.
A fifth object of the invention is to provide a pressure oil supply system of simple construction for a hydraulic device for use in vehicles having the hydraulic device, the system being adapted to render the vehicle compact and less costly.
To fulfill the foregoing objects, the present invention provides a transmission mechanism for a work vehicle having a differential gear unit, an HST and a drive source which are arranged in a body of the vehicle from longitudinal one side of the vehicle body, i.e., one side thereof in a first direction, toward the other side thereof in a second direction so as to drive axles positioned toward said one side, the vehicle having a work device disposed externally of the vehicle body toward the first direction, the transmission mechanism being characterized in that the mechanism comprises:
a travel power transmission path for transmitting power from the drive source to the differential gear unit via the HST, and a PTO power transmission path for dividedly transmitting the power from the travel power transmission path to a PTO unit for driving the work device,
the travel power transmission path further comprising a transmission for transmitting an output of the HST to the differential gear unit,
the transmission constituting a portion of the travel power transmission path and having a casing, and an input portion for receiving the power from the drive source, an output portion coupled to the differential gear unit and a travel cooperative mechanism coupling the input portion to the output portion which are housed in the casing,
the HST comprising a hydraulic pump having a pump shaft extending longitudinally of the vehicle body, a hydraulic motor having a motor shaft rotatable in cooperation with the hydraulic pump, and an HST housing accommodating the hydraulic pump and the hydraulic motor therein, the pump shaft having one end extending outward from the HST housing in the second direction and being connectable to a shaft of the drive source, the motor shaft having one end extending in the first direction into the transmission casing and connected to the input portion of the transmission,
the PTO unit comprising a PTO shaft supported by the HST housing so as to extend from the HST housing in the first direction, and a PTO cooperative mechanism accommodated in the HST housing and coupling the pump shaft to the PTO shaft to provide the PTO power transmission path (first feature of the invention).
To fulfill the foregoing objects, the present invention also provides a transmission mechanism comprising a differential gear unit, an HST and a drive source which are arranged in a body of a vehicle from longitudinal one side of the vehicle body, i.e., one side thereof in a first direction, toward the other side thereof in a second direction so as to drive axles positioned toward said one side, the transmission mechanism being characterized in that:
the HST comprises a hydraulic pump having a pump shaft extending longitudinally of the vehicle, a hydraulic motor cooperative with the hydraulic pump and having a motor shaft disposed in parallel to the pump shaft, and a housing accommodating the hydraulic pump and the hydraulic motor therein,
the hydraulic pump being adapted to receive power from the drive source by the pump shaft at an end thereof toward the second direction,
the hydraulic motor being adapted to output a driving force to be delivered to the differential gear unit from the motor shaft at an end thereof toward the first direction and to output a driving force to be delivered to wheels toward the second direction from the motor shaft at an end thereof toward the second direction (second feature of the invention).
To fulfill the foregoing objects, the present invention further provides a transmission mechanism for a vehicle so adapted that power from a drive source installed in a body of the vehicle is transmitted to a travel device and a PTO unit via an HST disposed outwardly of the drive source in a longitudinal direction of the vehicle, the transmission mechanism being characterized in that:
the mechanism comprises the HST for receiving a driving force from the drive source, and the PTO unit for receiving an output from the HST,
the PTO unit comprising a PTO shaft, a hydraulic clutch for effecting or interrupting power transmission to the PTO shaft, a charge pump for supplying a hydraulic fluid to the clutch, and a hydraulic circuit for interconnecting the clutch and the charge pump,
the HST comprising a hydraulic pump having a pump shaft extending longitudinally of the vehicle and connected at an inward end thereof to a shaft of the drive source, a hydraulic motor having a motor shaft rotatable in cooperation with the hydraulic pump, and a housing accommodating the hydraulic pump and the hydraulic motor therein, the pump shaft having an outward end projecting from the housing outward longitudinally of the vehicle, the housing having a main body accommodating the hydraulic pump and the hydraulic motor therein, and an extension extending outward widthwise of the vehicle from a side of the main body at which side the hydraulic pump is positioned,
the charge pump having a casing liquid-tightly surrounding the projection of the pump shaft and being adapted to perform a pumping action for the clutch by the rotation of the pump shaft,
the PTO shaft being supported by the housing extension longitudinally of the vehicle and having an outer end projecting outward longitudinally of the vehicle,
the hydraulic clutch being supported by the PTO shaft within the housing extension (third feature of the invention).
To fulfill the foregoing objects, the present invention further provides a pressure oil supply system for a vehicle comprising a hydraulic device,
the vehicle being so adapted that power from a drive source installed in a body of the vehicle is transmitted to a drive axle via an HST disposed adjacently to the drive source along the longitudinal direction of the vehicle and via a differential gear device coupled to the HST along said longitudinal direction,
the HST comprising an HST pump having a pump shaft extending longitudinally of the vehicle and connected to the drive source by a shaft, an HST motor cooperative with the hydraulic pump and having a motor shaft, and a housing accommodating the HST pump and the HST motor therein,
the differential gear device having a casing supporting the drive axle, and a differential gear unit housed in the casing and operatively connected to the motor shaft,
the pressure oil supply system being characterized in that the system comprises:
a hydraulic pump having a drive shaft supported by the housing so as to cause one end thereof to project outward from the housing, and a pump case formed continuously with the housing so as to liquid-tightly surround the projecting end of the drive shaft, the hydraulic pump being adapted to perform a pumping action by the rotation of the drive shaft,
a hydraulic output cooperative mechanism coupling the pump shaft of the HST pump to the drive shaft,
an intake line having one end connected to the casing of the differential gear device and the other end connected to the pump case, and
a discharge line having one end connected to the pump case and the other end connected to the hydraulic device (fourth feature of the invention).
The transmission mechanism can be so characterized that the HST comprises a hydraulic pump having a pump shaft extending longitudinally of the vehicle, a hydraulic motor cooperative with the hydraulic pump and having a motor shaft disposed in parallel to the pump shaft, and a housing accommodating the hydraulic pump and the hydraulic motor therein, the housing having walls spaced apart from each other and positioned toward the first direction and toward the second direction respectively, the transmission further comprising, between the first-direction wall and the second direction wall, a PTO unit, and a PTO power transmission path for transmitting devidedly to the PTO unit the power to be delivered from the drive source to the HST.
Alternatively, the transmission mechanism can be so characterized that the HST comprises a hydraulic pump having a pump shaft extending longitudinally of the vehicle for receiving a driving force from the drive source, a hydraulic motor cooperative with the hydraulic pump and having a motor shaft disposed in parallel to the pump shaft for outputting a driving force for travel, and a housing accommodating the hydraulic pump and the hydraulic motor therein, the housing having a space accommodating the pump and the shaft therein and serving as a reservoir for lubricating oil, the housing further accommodating a PTO unit, and a PTO power transmission path for transmitting devidedly to the PTO unit the power to be delivered from the drive source to the HST, the PTO unit comprising a clutch for effecting or interrupting transmission of the driving force.